I used to be a heavy smoker, at the height of my habit I could smoke 2+ packs a day. It was bad. When I finally decided to quit, I went cold turkey. For a week or two I had strong but manageable cravings, however they started to fade away and eventually the smell of cigarette smoke started being really unpleasant. Years on and I feel no pull towards tobacco and the idea of smoking it is repulsive to me now.

This is of course anecdotal evidence, but you (you, a smoker reading this thinking about quitting) are not doomed to suffer cravings forever nor are predestined to fail, like the Mark Twain quote could make you believe. Perhaps there are people, who find it really difficult to quit, but it is also possible to completely move on. Just don't fixate on how hard it is and simply do it.